A. Field of the Invention
The present invention relates to a method for plugging a zone of a subterranean formation penetrated by a wellbore. More particularly, it relates to a plugging technique utilizing a resin system containing a thermosetting resin and a curing agent or catalyst therefor in a single treatment stage. Another aspect of the invention is a treating fluid which may be utilized in one embodiment of the method.
B. Description of the Prior Art
In the production of oil and gas from subterranean formations, it is often found that water is produced with the hydrocarbons. Various techniques are known to selectively alter the permeability of the formation to improve the production of hydrocarbons relative to the production of water. Such techniques are not always successful however. Some may prove effective for a period of time, but eventually, the ratio of water:oil produced may become so high that production from that interval is no longer economically practical. In other instances, the water production may be so severe even initially that selective plugging techniques are not effective. When any of these conditions exists, it is desirable to plug that zone of the formation completely and permanently. Frequently, however, it is desired to produce from the same well at a different depth.
Various techniques have been proposed for permanently plugging a zone of a formation.
One technique which has been employed is to squeeze a cement slurry into the formation opposite the perforations adjacent the formation zone to be plugged. This technique requires waiting for the cement to set and thereafter drilling out the set cement remaining in the borehole. Furthermore, since the cement slurry contains a large amount of particulate material, it is not possible to obtain much depth of penetration into the formation.
Basically three approaches to chemically plugging a zone have been proposed. One approach is to consecutively inject into the formation, materials which react in situ to form a plug. A serious drawback of this technique, however, is that it is difficult to assure adequate mixing of the reactants since at least to some extent, one fluid tends to displace another within the formation rather to mix with it. A second approach to chemical plugging is to inject materials which will react with formation substances such as brine, sand particles, clays, or other materials naturally present in the formation. Again, however, the reliability of such techniques has not always been completely satisfactory.
The third basic approach to chemically plugging a formation has involved injecting previously mixed materials--e.g. a resin system containing both resin and a crosslinker or catalyst therefore in a single stage--into the formation where conditions such as time, temperature, and/or pressure will trigger a plug-forming reaction. A serious drawback of such systems, however, has been the need to come in with a drilling rig to clean out residual material which sets in the wellbore. For example, Robichaux, U.S. Pat. No. 3,308,884 teaches use of an amine catalyzed epoxy resin system for such a plugging operation, but teaches at column 7, lines 54-61 that after the resin has set, the remaining resin in the borehole can be drilled out and further drilling of the well can be resumed. The need to drill the material out of the wellbore significantly increases the cost of a treatment because of the need to erect a drilling rig--especially where an offshore well is involved.